1. Field of the Invention
This invention relates generally to cordless telephones. More particularly, it relates to cordless telephones having improved audio feedback control, especially when the cordless telephone is operating in a speakerphone mode.
2. Background of Related Art
Many cordless telephones come with a speakerphone built into the base. The user typically has the ability to carry on a conversation using the handset alone, or using the base unit alone as a speakerphone. Many cordless telephones permit both the handset and the base unit to be operated simultaneously, allowing one person to participate in a telephone call using the handset while another person participates using the base unit.
The physical environment of the cordless telephone may cause direct or indirect audible echoes in the audio signals between the handset and the base unit. For instance, a primary source of acoustical feedback is caused from sounds output by the speaker of the base unit operating in a speakerphone mode being picked back up by a microphone in the handset. This most frequently occurs when the output sound bounces off the ceiling, walls and other structures in the room. A secondary source of acoustic feedback results from sounds output from the handset and picked up by the base unit.
As many users of such a cordless telephone know, acoustical feedback typically causes uncomfortable feedback such as squealing in the signal output from the speaker. Thus, care must be taken when using both the handset and the base unit simultaneously to maintain a safe distance between the simultaneously operating handset and base unit to avoid acoustic feedback.
However, even with the risk of acoustic feedback causing a howl, there may be times when it is desired to have both the handset and the base unit operating in close proximity. For instance, if the user of the handset is moving about a room, and passes by the base unit simultaneously operating as a speakerphone.
FIG. 7 shows a conventional base unit 700 and handset 702 of a cordless telephone during an acoustical feedback scenario.
In particular, as shown in FIG. 7, both the handset 702 and the base unit 700 are operating simultaneously in close proximity to one another. This causes primary acoustical feedback from sound output by the speaker 760 of the base unit being picked up by the microphone 752 of the handset 702, and even in some cases secondary feedback from sound output by the speaker 750 of the handset being picked up by the microphone 762 of the base unit 700. These are relatively low loss feedback paths which may become unstable, cause howling from the speaker of the base unit and/or from the speaker of the remote handset.
Some cordless telephones include acoustic echo cancellers (AECs). Conventional acoustical echo cancellers suppress audio picked up by a microphone which was output by a speaker on the same telephone. These conventional AECs are typically adaptive, speech trained and monitored and adjusted as necessary for optimal performance.
AECs typically perform well with acoustic reflections off a wall or ceiling, but operate less effectively and even not at all when trying to overcome the acoustic feedback problems associated with the howl caused when an operating handset comes within close proximity of its base unit while in speakerphone mode.
The same problems are associated with a handset of a cordless telephone which is capable of operating in a speakerphone mode.
There is a need for apparatus and methods for reducing or eliminating the risk or danger of acoustical feedback in cordless telephones.